1. Field
Embodiments and implementations of the present invention relate generally to image-transferring arrays such as fiber optic faceplates and other optical fiber imaging and light-transmitting devices, and more particularly to the inclusion of integral contrast enhancement in such devices.
2. Brief Description of an Illustrative Environment and Related Art
The transmission of light and images through bundles comprised of flexible or adjacently fused light-conductive elements (e.g., optical fibers) is an established art. Image conduits such as inverters, tapers and “straight-throughs” are well known to practitioners of the optical fiber arts. Fused optical fiber image conduits find broad application as components in such devices as night visions goggles, rifle scopes, x-ray detectors and medical imaging apparatus, by way of non-limiting example.
The inclusion of light-absorbing materials (e.g., glasses) into fused optical components such as fiber optic faceplates, straight-throughs and tapers in order to suppress cross-talk, enhance contrast and control numerical aperture is widely known in the optical fiber industry. These absorbing materials, alternatively referred to as Extra-Murual Absorption (EMA) materials, media, glasses, fibers, filaments and rods, as indicated by context, are typically incorporated in accordance with one or more of three general methods. According to a first approach, an absorptive coating—or even a sleeve or tube—is applied to the outside of each constituent waveguide individually, yielding what is referred to as a “circumferential EMA.” A cross-sectional view of an illustrative fiber bundle including fibers with circumferential EMA material is shown in FIG. 1A. With reference to FIG. 1B, a second approach indicates the substitution of selected light-conductive elements (e.g., fibers) within a bundle with absorbing fibers, wherein the substitute fibers are referred to alternatively as “substitutional,” “replacement” or “statistical” EMA fibers. According to a third common approach, absorbing fibers are inserted into the interstitial packing vacancies in the fiber array. Examples of bundles including such fibers—known as “interstitial EMA fibers”—are shown FIGS. 1C, 1D and 1E.
Although circumferential, interstitial and substitutional EMA media have met with varying degrees of success in suppressing cross talk due to the refraction and propagation of unwanted stray light, the need for black glass tubing and/or individual EMA fibers, in various configurations, invariably adds to the complexity and expense of fabrication and, furthermore, can introduce aberrations into transferred images. Moreover, the introduction of different glass compositions in an array increases the potential for adverse interactions between incompatible glasses. A still further limitation of incorporating glass-based EMA elements into imaging or illumination bundles is that they must be incorporated into the structure early in the process and their light-absorbing capacity cannot be adjusted once they are incorporated.
Accordingly, there exists a need for light-transmissive optical components incorporating extramural-absorbing materials that (i) are not glass-based and (ii) have adjustable light-absorption characteristics.